The present invention is directed generally to novel systems and methods for performing sputter deposition, and to optical devices manufactured using such systems and methods.
Conventional pulsed target plasma sputtering systems generate their plasma via application of 10 to 500 kHz pulsed DC power to a sputter target. Most commonly, magnetic fields of several times 0.01 Telsa are disposed proximate to the target to intensify the plasma formed. During negative pulses, ions drawn from the plasma sputter the target, and material from the target is deposited on a substrate. It is believed that electrons from the plasma neutralize charge on the target during parts of the pulse cycle when the negative voltage is off. It is believed that in a conventional pulsed-target plasma sputtering apparatus, the target pulsing power supply must provide a high-voltage leading edge, for the purpose of ignition of the plasma, on every pulse. While it is believed that a system comprising the application of a-symmetric bi-polar DC pulse signals for such a purpose is known, such systems in the prior art require complicated circuitry and such systems fail to provide means for independently controlling the ion currents and the electron currents at the target. Moreover, since the plasma ignition is partly a stochastic event/process, there is a degree of process uncertainty and instability. It would be beneficial to provide a system that provides better control of the process without adding complex circuitry to the apparatus arrangement.
It would also be beneficial to provide a system for independently controlling the ion and electron currents of multiple targets that are sputtered simultaneously to deposit a film. Furthermore, it would be beneficial to provide a system that minimized cross-contamination effects between targets when multiple targets are sputtered simultaneously.
The present invention is directed to a system for performing sputter deposition on a substrate. Biasing circuitry biases the target with an a-symmetric bi-polar DC voltage pulse signal. The biasing circuitry is formed from a positive voltage source with respect to ground, a negative voltage source with respect to ground and a high frequency switch. At least one current sensor, coupled to the biasing circuitry, monitors a positive current and a negative current from the target during one or more cycles of the a-symmetric bi-polar DC voltage pulse signal. A control system, coupled to the at least one current sensor, varies the ion current independently from the electron current. The ion and electron sources create a continuous plasma that is proximate the target and the biasing circuitry causes the target to alternately attract ions and electrons from the plasma. The ions attracted from the plasma sputter the target, and material from the target is deposited on the substrate. The electrons attracted from the plasma neutralize accumulated charge on the target. In one embodiment, the controller varies the a-symmetric bi-polar DC voltage pulse signal used to bias the target independently from the ion and electron currents. In this embodiment, target voltages and currents are tailored to optimize film deposition parameters.
In accordance with a further aspect, the present invention is directed to a multi-target system and method for performing sputter deposition, where at least one ion source generates ion current directed at first and second targets, and at least one electron source generates electron current directed at the first and second targets. In this embodiment, circuitry biases the first target with a first DC voltage pulse signal and the second target with a second DC voltage pulse signal that is independent of the first DC voltage pulse signal. The biasing circuitry is formed from at least one voltage source with respect to ground, a first high frequency switch used to form the first DC voltage pulse signal, and a second high frequency switch used to form the second DC voltage pulse signal. A first current sensor, coupled to the biasing circuitry, monitors a positive current and a negative current from the first target during one or more cycles of the first DC voltage pulse signal, and a second current sensor, coupled to the biasing circuitry, monitors a positive current and a negative current from the second target during one or more cycles of the second DC voltage pulse signal. A controller, coupled to the first and second current sensors, varies the ion current independently from the electron current. The at least one ion source and the at least one electron source create a continuous plasma proximate the first and second targets, and the biasing circuitry causes the first and second targets to alternately attract ions and electrons from the plasma. The ions attracted from the plasma sputter the first and second targets and material from the first and second targets is deposited on a substrate. The electrons attracted from the plasma neutralize accumulated charge on the first and second targets.
In accordance with embodiment of the above multi-target invention, material from the first target deposited on the substrate corresponds to a first component of an alloy/compound, and material from the second target deposited on the substrate corresponds to a second component of the alloy/compound. In this embodiment, the controller varies a composition ratio of the first and second components of the alloy/compound deposited on the substrate by independently varying a number of negative pulses per unit time in each of the first and second bi-polar DC voltage pulse signals. The controller optionally varies the composition ratio over time such that the composition ratio of alloy/compound deposited on the substrate varies throughout a thickness of a film deposited on the substrate. For example, the controller can vary the process parameters over time such that the composition ratio of alloy/compound deposited on the substrate varies linearly, in a sinusoidal or parabolic fashion, as a step function, or in some other fashion throughout a thickness of a film deposited on the substrate.
In accordance with a still further aspect of the above multi-target invention, the face of the first target is arranged such that it is outside of a line-of-sight of the face of the second target, and the face of the second target is outside of a line-of-sight of the face of the first target.
In accordance with a still further aspect of the above multi-target invention, multiple ion and electron sources are used to supply independent ion and electron currents to each of the targets. In this embodiment, a first ion source generates a first ion current directed at the first target and a second ion source generates a second (independent) ion current directed at the second target, a first electron source generates a first electron current directed at the first target and a second electron source generates a second (independent) electron current directed at the second target. In this embodiment, the controller varies the first ion current independently from the first electron current, and the controller varies the second ion current independently from the second electron current.